It is a single speed t case used in Fords behind four speeds with granny low first gears. The idea is the 6.5 (or so) ratio in first would be equal to a standard first with a two speed t case.
They are plenty strong, but you will find a large jump from first to second when offroading.

FWIW-
I had a 66 F-100 that I used as a plow truck for many years. I split 2 of those tcases right down the middle, The first one was so bad that the lower portion of the case was completely broken off & hanging by the front driveshaft. Keep in mind that this was in a 6000 lb truck, with a strong 390, plowing snow.
After the 2nd one I put in a NP435/NP205 combo...no more worries
IMO it's only useful as a paperweight...

__________________
"It's better to have loved and lost, than to live with a psycho the rest of your life"

I have herd of them splitting under extreme uses like your plowing or an f-100 on 37" tires with a big block on rocks. Maybe ill run it until i can afford to adapt it to my np231; or if my np205 will even fit